Each “pipe” of the Organ Pipe Mud Dauber nest consists of several sealed cells (four, in this photograph), each stuffed with spiders (typically orb-spinning spider species) and one wasp egg. When the egg hatches, the white wasp larva consumes the paralyzed spiders, which are still fresh because they are still alive. Eventually, upon finishing the spiders, the larva will form a pupa case, and spend the winter inside it. In the spring the adult wasp will emerge from the case and chew its way out of the mud cell. If you look closely at the open, back side of these three “pipes” you can see that the oldest pipe is on the left, and contains cells with wasp larvae, whereas you can see mud dauber eggs lying on top of the spiders in two of the cells on the far right, in the most recently built pipe.